编辑距离问题

代码说明：

说明：  设A和B是2个字符串。要用最少的字符操作将字符串A转换为字符串B。这里所说的字符操作包括：1）删除一个字符；2）插入一个字符；3）将一个字符改为另一个字符。将字符串A变换为字符串B所用的最少字符操作称为字符串A到B的编辑距离，记为d（A，B）(Let A and B be two strings. String A is converted to string B with the least number of character operations. The character operations mentioned here include: 1) deleting a character; 2) inserting a character; 3) changing one character to another character. The minimum character operation used to convert string A to string B is called the editing distance from string A to B, which is denoted D D as D (A, B).)